Threat of Over-fishing in the Mekong

Despite the productivity of the Mekong, the threat of over-fishing is high because of the huge scale of subsistence fishing, the majority of which goes unrecorded, as well as poor fishing practices. In basins around the world, inland fisheries are "under-reported by 2-3 times", so their contribution to direct human consumption is likely to be at least twice as high as the reported fish catch.

Subsistence fishing in the Mekong is heavy and destructive, and there is evidence of declining fish populations as a result. Most important however is evidence of the loss of community structure, i.e. assemblage over-fishing, where entire biological groups of fish, not just individual species, start to disappear.

Several Mekong fish species are now endangered and both the number and size of fish caught has steadily declined. In fact, recent data demonstrates a pattern of increasing catch and increasing fishing effort followed by a declining catch with a sustained effort, typical of an over-exploited population.

For instance, a century ago, the Mekong Giant Catfish was found along the entire length of the river from Vietnam to southern China. Since then, however, populations have dropped precipitously. Scientists estimate that the total number of Mekong Giant Catfish has decreased about 90% in just the past two decades.

WWF recently helped broker a voluntary ban on this species with Thai fishers. In Laos as early as 1890, a large fishery developed for the Mekong Giant Catfish but by 1940, declines were observed in northeast Thailand.

Large fish species including the Mekong giant catfish, the river catfish, the giant carp, and the giant stingray in the Mekong are in decline, indicating possible 'assemblage overfishing'.

In the Mekong, uncertain fishing rights, over-fishing and illegal fishing have taken a heavy toll on fish stocks. People illegally use small-meshed mosquito nets to capture fish (which catch juveniles as well as adult fish), electro-shock fish with car batteries, and increasingly over-harvest fish with poison. Inherited from colonial times, the Cambodian government has managed its fisheries according to a concession system that enables unfair access, corruption and occasionally violent disputes.

The productivity of the Mekong River underscores the importance of this region in providing millions with food, but creates the misleading impression that its resources are limitless. It is clear, however, that unsustainable fishing practices and levels of harvest, along with changes in water flows induced by new dams, threaten the permanence of this wealth.